Aberration corrected analytical electron microscopy studies of sol-immobilized Au + Pd, Au{Pd} and Pd{Au} catalysts used for benzyl alcoholoxidation and hydrogen peroxide production

Abstract

In this study, a systematic series of AuPd bimetallic particles were prepared by colloidal synthesis methods, in order to gain better control over the particle size distribution and structure. Particles having random alloy structures, as well as ‘designer’ particles with Pd-shell/Au-core and Au-shell/Pd-core morphologies, have been prepared and immobilized on both activated carbon and TiO₂ supports. Aberration corrected analytical electron microscopy (ACEAM) has been extensively used to characterize these sol-immobilized materials. In particular, state-of-the-art z-contrast STEM-HAADF imaging and STEM-XEDS spectrum imaging has been employed. These techniques have provided invaluable new (and often unexpected) information on the atomic structure, elemental distribution within particles, and compositional variations between particles for these controlled catalyst preparations. In addition, we have been able to compare their differing thermal stability, sintering and wetting behaviors on activated carbon and TiO₂ supports. These sol immobilized materials have also been compared as catalysts for (i) benzyl alcohol oxidation and (ii) the direct production of H₂O₂ in an attempt to elucidate the optimum particle morphology/support combination for each reaction.